Mems gyroscope

ABSTRACT

A MEMS gyroscope is disclosed herein, wherein the MEMS gyroscope comprised a magnetic sensing mechanism and a magnetic source that is formed at the proof-mass, wherein the magnetic sensing mechanism comprises an integrated pickup coil of a fluxgate. A magnetic shield is provided in the vicinity of the magnetic source.

CROSS-REFERENCE

This US utility patent application claims priority from co-pending USutility patent application “A HYBRID MEMS DEVICE,” Ser. No. 13/559,625filed Jul. 27, 2012, which claims priority from US provisional patentapplication “A HYBRID MEMS DEVICE,” filed May 31, 2012, Ser. No.61/653,408 to Biao Zhang and Tao Ju. This US utility patent applicationalso claims priority from co-pending US utility patent application “AMEMS DEVICE,” Ser. No. 13/854,972 filed Apr. 2, 2013 to the sameinventor of this US utility patent application, the subject matter ofeach of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD OF THE DISCLOSURE

The technical field of the examples to be disclosed in the followingsections is related generally to the art of operation ofmicrostructures, and, more particularly, to operation of MEMS devicescomprising MEMS magnetic sensing structures.

BACKGROUND OF THE DISCLOSURE

Microstructures, such as microelectromechanical (hereafter MEMS) devices(e.g. accelerometers, DC relay and RF switches, optical cross connectsand optical switches, microlenses, reflectors and beam splitters,filters, oscillators and antenna system components, variable capacitorsand inductors, switched banks of filters, resonant comb-drives andresonant beams, and micromirror arrays for direct view and projectiondisplays) have many applications in basic signal transduction. Forexample, a MEMS gyroscope measures angular rate.

A gyroscope (hereafter “gyro” or “gyroscope”) is based on the Corioliseffect as diagrammatically illustrated in FIG. it. Proof-mass 100 ismoving with velocity V_(d). Under external angular velocity Ω, theCoriolis effect causes movement of the poof-mass (100) with velocityV_(s). With fixed V_(d), the external angular velocity can be measuredfrom V_(d). A typical example based on the theory shown in FIG. 1 iscapacitive MEMS gyroscope, as diagrammatically illustrated in FIG. 2.

The MEMS gyro is a typical capacitive MEMS gyro, which has been widelystudied. Regardless of various structural variations, the capacitiveMEMS gyro in FIG. 2 includes the very basic theory based on which allother variations are built. In this typical structure, capacitive MEMSgyro 102 is comprised of proof-mass 100, driving mode 104, and sensingmode 102. The driving mode (104) causes the proof-mass (100) to move ina predefined direction, and such movement is often in a form ofresonance vibration. Under external angular rotation, the proof-mass(100) also moves along the V_(s) direction with velocity V_(s). Suchmovement of V_(s) is detected by the capacitor structure of the sensingmode (102). Both of the driving and sensing modes use capacitivestructures, whereas the capacitive structure of the driving mode changesthe overlaps of the capacitors, and the capacitive structure of thesensing mode changes the gaps of the capacitors.

Current capacitive MEMS gyros, however, are hard to achievesubmicro-g/rtHz because the capacitance between sensing electrodesdecreases with the miniaturization of the movable structure of thesensing element and the impact of the stray and parasitic capacitanceincrease at the same time, even with large and high aspect ratioproof-masses.

Therefore, what is desired is a MEMS device capable of sensing angularvelocities and methods of operating the same.

SUMMARY OF THE DISCLOSURE

In view of the foregoing, a MEMS gyroscope is disclosed herein, whereinthe gyroscope comprises: a first substrate, comprising: a movableportion that is movable in response to an external angular velocity; amagnetic source for generating magnetic field; and a magnetic shield inthe vicinity of the magnetic source; a second substrate having amagnetic sensor for detecting the magnetic field from said magneticsource, wherein the magnetic sensor is a pickup coil of a fluxgate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 diagrammatically illustrates the Coriolis effect in a MEMSstructure;

FIG. 2 is a top view of a typical existing capacitive MEMS gyroscopehaving a driving mode and a sensing mode, wherein both of the drivingand sensing mode utilize capacitance structures;

FIG. 3 illustrates an exemplary MEMS gyroscope having a magnetic sensingmechanism;

FIG. 4 illustrates a top view of a portion of an exemplaryimplementation of the MEMS gyroscope illustrated in FIG. 3, wherein theMEMS gyroscope illustrated in FIG. 4 having a capacitive driving modeand a magnetic sensing mechanism;

FIG. 5 illustrates a perspective view of a portion of another exemplaryimplementation of the MEMS gyroscope illustrated in FIG. 3, wherein theMEMS gyroscope illustrated in FIG. 5 having a magnetic driving mechanismfor the driving mode and a magnetic sensing mechanism for the sensingmode

FIG. 6 illustrates an exemplary magnetic driving mechanism of the MEMSgyroscope in FIG. 5;

FIG. 7 illustrates an exemplary magnetic source of the MEMS gyroscopeillustrated in FIG. 3;

FIG. 8 illustrates an exemplary magnetic sensing mechanism that can beused in the MEMS gyroscope illustrated in FIG. 3;

FIG. 9 illustrates an exemplary MEMS gyroscope having multiple magneticsensing mechanisms; and

FIG. 10 illustrates another exemplary MEMS gyroscope comprising amagnetic field shield for enhancing measurements of the magnetic signal.

DETAILED DESCRIPTION OF SELECTED EXAMPLES

Disclosed herein is a MEMS gyroscope for sensing an angular velocity,wherein the MEMS gyroscope utilizes a magnetic sensing mechanism. Itwill be appreciated by those skilled in the art that the followingdiscussion is for demonstration purposes, and should not be interpretedas a limitation. Many other variations within the scope of the followingdisclosure are also applicable. For example, the MEMS gyroscope and themethod disclosed in the following are applicable for use inaccelerometers.

Referring to FIG. 3, an exemplary MEMS gyroscope is illustrated herein,In this example, MEMS gyroscope 106 comprises magnetic sensing mechanism114 for sensing the target angular velocity through the measurement ofproof-mass 112. Specifically, MEMS gyroscope 106 comprisesmass-substrate 108 and sensor substrate 110. Mass-substrate 108comprises proof-mass 112 that is capable of responding to an angularvelocity. The two substrates (108 and 110) are spaced apart, forexample, by a pillar (not shown herein for simplicity) such that atleast the proof-mass (112) is movable in response to an angular velocityunder the Coriolis effect. The movement of the proof-mass (112) and thusthe target angular velocity can be measured by magnetic sensingmechanism 114.

The magnetic sensing mechanism (114) in this example comprises amagnetic source 116 and magnetic sensor 118. The magnetic source (116)generates a magnetic field, and the magnetic sensor (118) detects themagnetic field and/or the magnetic field variations that is generated bythe magnetic source (116). In the example illustrated herein in FIG. 3,the magnetic source is placed on/in the proof-mass (112) and moves withthe proof-mass (112). The magnetic sensor (118) is placed on/in thesensor substrate (120) and non-movable relative to the moving proof-mass(112) and the magnetic source (116). With this configuration, themovement of the proof-mass (112) can be measured from the measurement ofthe magnetic field from the magnetic source (116).

Other than placing the magnetic source on/in the movable proof-mass(1112), the magnetic source (116) can be placed on/in the sensorsubstrate (120); and the magnetic sensor (118) can be placed on in theproof-mass (112).

It is also noted that the MEMS gyroscope illustrated in FIG. 3 can alsobe used as an accelerometer.

The MEMS gyroscope as discussed above with reference to FIG. 3 can beimplemented in many ways, one of which is illustrated in FIG. 4.Referring to FIG. 4, the proof-mass (120) is driven by capacitive, suchas capacitive comb. The sensing mode, however, is performed using themagnetic sensing mechanism illustrated in FIG. 3. For this reason,capacitive combs can be absent from the proof-mass (120).

Alternatively, the proof-mass can be driven by magnetic force, anexample of which is illustrated in FIG. 5. Referring to FIG. 5, the masssubstrate (108) comprises a movable proof-mass (126) that is supportedby flexible structures such as flexures 128, 129, and 130. The layout ofthe flexures enables the proof-mass to move in a plane substantiallyparallel to the major planes of mass substrate 108. In particular, theflexures enables the proof-mass to move along the length and the widthdirections, wherein the length direction can be the driving modedirection and the width direction can be the sensing mode direction ofthe MEMS gyro device. The proof-mass (126) is connected to frame 132through flexures (128, 129, and 130). The frame (132) is anchored bynon-movable structures such as pillar 134. The mass-substrate (108) andsensing substrate 110 are spaced apart by the pillar (134). Theproof-mass 12) in this example is driving by a magnetic drivingmechanism (136). Specifically, the proof-mass (126) can move (e.g.vibrate) in the driving mode under magnetic force applied by magneticdriving mechanism 136, which is better illustrated in FIG. 6.

Referring to FIG. 6, the magnetic driving mechanism 136 comprise amagnet core 138 surrounded by coil 140. By applying an alternatingcurrent through coil 140, an alternating magnetic field can be generatedfrom the coil 140. The alternating magnetic field applies magnetic forceto the magnet core 140 so as to move the magnet core. The magnet corethus moves the proof-mass.

The magnetic source (114) of the MEMS gyroscope (106) illustrated inFIG. 3 can be implemented in many ways, one of which is illustrated inFIG. 7. Referring to FIG. 7, conductive wire 142 is displaced on/inproof-mass 112. In one example, conductive wire 142 can be placed on thelower surface of the proof-mass (112), wherein the tower surface isfacing the magnetic sensors (118 in FIG. 3) on the sensor substrate(110, in FIG. 3). Alternatively, the conductive wire (142) can be placedon the top surface of the proof-mass (112), i.e. on the opposite side ofthe proof-mass (112) in view of the magnetic sensor (118). In anotherexample, the conductive wire (142) can be placed inside the proof-mass,e.g. laminated or embedded inside the proof-mass (112), which will notbe detailed herein as those examples are obvious to those skilled in theart of the related technical field.

The conductive wire (142) can be implemented in many suitable ways, oneof which is illustrated in FIG. 7. In this example, the conductive wire(142) comprises a center conductive segment 146 and tapered contacts 144and 148 that extend the central conductive segment to terminals, throughthe terminals of which current can be driven through the centralsegment. The conductive wire (142) may have other configurations. Forexample, the contact tapered contacts (144 and 148) and the centralsegment (146) maybe U-shaped such that the tapered contacts may besubstantially parallel hut are substantially perpendicular to thecentral segment, which is not shown for its obviousness.

The magnetic sensor (118) as shown in FIG. 3 can be a pickup coil of afluxgate, as illustrated in FIG. 8. Referring to FIG. 8, magnetic sensor118 is the pickup coil of fluxgate 117. The fluxgate (117) furthercomprises excitation coils 182 and 180 that are wired around magneticcore 170. The excitation coils 180 and 182 are wired in the oppositedirection to the pickup coil 118 such that the inducted magnetic fieldfrom the pickup coil 118 is in the opposite direction to the excitationcoils 180 and 182. The excitation coils are serially connected.Specifically, the output of one excitation coil (e.g. 180) is connectedto the input of the other excitation coil (e.g. 182). In operation,excitation current can be delivered into the excitation coils throughthe input 176 of excitation coil 180 and output from the output terminal178 of excitation coil 182. The voltage between the terminals 172 and174 of pickup coil 118 is measured to obtain the magnetic flux change.The motion of the proof-mass can be derived from such magnetic fluxchange. The fluxgate (117) as illustrated in FIG. 8 can be fabricated byusing MEMS technology and integrated in the sensor wafer (110) as shownin FIG. 3. The derivation of the proof-mass motion from the measuredmagnetic flux change is not discussed herein because of its obviousnessto the person skilled in the art.

The fluxgate can be implemented in many ways. In one example, the coilscan be composed of copper; and the magnetic core can be composed of NiFeand are fabricated on a silicon wafer (i.e. the sensor wafer).

In some applications, multiple magnetic sensing mechanisms can beprovided, an example of which is illustrated in FIG. 10. Referring toFIG. 10, magnetic sensing mechanisms 116 and 164 are provided fordetecting the movements of proof-mass 112. The multiple magnetic sensingmechanisms can be used for detecting the movements of proof-mass 112 indriving mode and sensing mode respectively. Alternatively, the multiplemagnetic sensing mechanisms 116 and 164 can be provided for detectingthe same modes (e.g. the driving mode and/or the sensing mode).

In another example, the MEMS gyroscope as discussed above with referenceto FIG. 3 can have magnetic field shield so as to increase magneticfield signal measurement, as illustrated in FIG. 10. Referring to FIG.10, magnetic field shields 186 and 188 can be disposed in the vicinityof magnetic field source 116. The magnetic field shields (186 and 188)may be composed of any suitable magnetic materials, such as nickel-ironalloys. The magnetic shields (186 and 188) can be formed by magneticsputtering or other suitable methods, which will not be discussedherein.

The magnetic field shields (186 and 188) can be in any suitable forms.In one example, the magnetic field shields (186 and 188) can be formedsuch that the gap between the shields is larger than the lateraldimension of the underlying magnetic sensor (118) so as to providesufficient space to allow the motion of proof-mass 112.

It will be appreciated by those of skilled in the art that a new anduseful MEMS gyroscope has been described herein. In view of the manypossible embodiments, however, it should be recognized that theembodiments described herein with respect to the drawing figures aremeant to be illustrative only and should not be taken as limiting thescope of what is claimed. Those of skill in the art will recognize thatthe illustrated embodiments can be modified in arrangement and detail.Therefore, the devices and methods as described herein contemplate allsuch embodiments as may come within the scope of the following claimsand equivalents thereof. In the claims, only elements denoted by thewords “means for” are intended to be interpreted as means plus functionclaims under 35 U.S.C. §112, the sixth paragraph.

We claim:
 1. A MEMS gyroscope, comprising: a first substrate,comprising: a movable portion that is movable in response to an externalangular velocity; a magnetic source for generating magnetic field; and amagnetic shield in the vicinity of the magnetic source; a secondsubstrate having a magnetic sensor for detecting the magnetic field fromsaid magnetic source, wherein the magnetic sensor is a pickup coil of afluxgate.
 2. The MEMS gyroscope of claim 1, wherein the magnetic sourcecomprises a conducting wire.
 3. The MEMS gyroscope of claim 1, whereinthe magnetic source comprises a magnetic nanoparticle.
 4. The MEMSgyroscope of claim 2, wherein the magnetic sensor comprises agiant-magnetic-resistor.
 5. The MEMS gyroscope of claim 2, wherein themagnetic sensors comprises a spin-valve structure.
 6. The MEMS gyroscopeof claim 2, wherein the magnetic sensors comprises atunnel-magnetic-resistor.
 7. The MEMS gyroscope of claim 2, wherein themagnetic sensors comprises a magnetic pickup coil that is an element ofa fluxgate.